The present invention relates, generally, to a method and apparatus for dislodging deposits from a vessel and, more specifically, to as method for dislodging deposits from a vessel using a gas impulse device.
In the handling and storage of particulate solids, problems are encountered in various items of equipment. Most common of these items of equipment is the silo, generally a large, vertical, cylindrical vessel with a conical base fitted with an outlet valve mechanism. The term silo is, however, often used interchangeably with any of the terms bin, tank and bunker. Shapes vary, including those having square or rectangular cross-section and those with flat, pyramidal or dished bases.
A common problem occurring in silos as well as in other solid handling equipment is the accretion of particulate solids which eventually gives rise to reduced flow through the vessel or, in extreme cases, to complete blockage of the vessel.
In more serious cases of agglomeration, the flow from a vessel is partially or totally restricted by bridging of solids across the vessel outlet. Another, similar, problem is referred to as xe2x80x9crat-holing,xe2x80x9d which also results in restricted flow from a vessel. When there occurs a severe build up of accumulated solids, specialized apparatus is generally required to remove the build-up. There are known in the art, mechanical methods for solving problems of undesired accumulation of solids. By way of example, where an undesirable accumulation of particulate matter is easily accessible, a hammer and chisel (manual or pneumatic) may be used to fracture and remove the agglomerated particles.
In the case of closed vessels with restricted manual access, such as a large silo, there are several known cleaning methods available. One method utilizes a device commonly referred to in the art as a xe2x80x9cwhip.xe2x80x9d This device is pneumatically or hydraulically driven, and consists of a cutting head supported from the roof opening of a silo. The cutting head rotates rapidly so that flail chains attached to the head repeatedly strike the layer of accumulated material while the head is progressively translated upward or downward within the silo. This process is generally slow and rather cumbersome, and often poses a risk of damage to the silo being treated.
Other devices well known in the art for preventing or removing build-up of solids in flow through systems are air cannons and vibrators. Air cannons are, however, only moderately efficient for breaking up bridging and ineffective for overcoming rat-holing. Vibrators are only minimally effective for overcoming both bridging and rat-holing.
Apart from being time consuming and wasteful of resources, the implementation of such mechanical methods is generally known to be problematic. Furthermore, such mechanical processes are often known to create risk of dust explosion or fire, particularly when carried out in dusty environments. Where food or medicinal environments are concerned, such mechanical cleaning methods also give rise to considerations of hygiene. There also exists the possibility of emission of undesirable or harmful gases.
Referring to U.S. Pat. No. 4,571,138 to Farajun, entitled xe2x80x9cApparatus For Silo Clean Out,xe2x80x9d there is described apparatus for cleaning solids that have accumulated in places of restricted access such as silos, hoppers and the like. This cleaning apparatus includes a power driven device for impacting the accumulated material and allowing it to fall away. The device for impacting the solids is suspended from and powered by a cable and hose combination, which is reeled onto a drum supported above the material in the silo. The drum is rotatable to reel-out or reel-in the cable and hose to position the impacting device in the vicinity of the material to be removed. The apparatus includes provision for automatically reversing the impacting device along the material face and, in the event of a material avalanche, for releasing the drum to allow the impacting device to fall downwardly with the flowing material in the silo.
Referring now to U.S. Pat. No. 4,881,856 to Greig, entitled xe2x80x9cChip Snake,xe2x80x9d there is described a cleaning device for loosening and removing accumulated material, such as wood chips, in silos, using a raking action of regularly spaced spikes and a flailing action of a hose with a jet stream nozzle. The device includes a hose, connected to a compressed air supply, and a nozzle at the end of the hose. Compressed air is passed through the hose and exits the nozzle causing the nozzle and hose to move under the influence of the expelled compressed air. Spikes are attached along the hose to provide regularly spaced raking elements. Anti-kink mechanisms maintain the hose in a straight alignment. The operation involves lowering the nozzle into a silo in the vicinity of agglomerated material. Then compressed air is introduced into the hose and expelled out of the nozzle in a jet stream, thereby causing the hose and nozzle to move about in the silo, so that the spikes strike and dislodge the impacted material.
Further, referring to U.S. Pat. No. 4,942,982 to Hartwigsen, et al., entitled xe2x80x9cSilo Cleaning Apparatus,xe2x80x9d there is described apparatus for cleaning a silo which has a mass of agglomerated particles. Dislodging the accumulated mass is achieved by extending at least one flexible tube connected to a bludgeon into the silo near to the accumulated mass and introducing gas through the tube and bludgeon at a rate and pressure that causes swinging and writhing movements by the bludgeon and tube.
Referring also to U.S. Pat. No. 5,649,338 to Kato, entitled xe2x80x9cAutomatic Interior Cleaning System For A Powdered Material Processing Device,xe2x80x9d there is described an automatic interior cleaning system for processing equipment for handling finely divided material. The equipment requiring cleaning includes interior surfaces of, for example, silos, mixers, and dust collectors. A compressor and a gas storage tank supply gas, preferably air, at a sufficient pressure to dislodge residues of materials that collect on interior surfaces. A valve connecting the gas tank to a cleaning-nozzle tube opens and closes, supplying pulses of air to the cleaning nozzle tube. The cleaning nozzle tube delivers the pulses through slots in the tube to the inner surface of the equipment requiring cleaning. The pressurized air pulses produce shock waves, which dislodge any residues from the interior surface. Automatic removal of residues during processing prevents contamination of subsequently processed materials.
Other known processes for the cleaning of closed vessels utilize liquid carbon dioxide for effecting cavitation erosion of accumulated solids. Such processes are employed where mechanical methods pose a risk of flammability.
Referring to U.S. Pat. No. 5,316,591 to Chao, et al., entitled xe2x80x9cCleaning By Cavitation In Liquefied Gas,xe2x80x9d there is described the removal of undesired material from a chosen substrate by a process comprising placing the substrate containing the undesired material in a cleaning chamber provided with means for causing cavitation. The process involves introducing a liquefied gas, such as liquid carbon dioxide, into the cleaning chamber in contact with the substrate containing the undesired material, with the liquid carbon dioxide at a temperature below its critical temperature. Exposing the liquid carbon dioxide to the cavitation-producing means for a period of time is sufficient to remove the undesired material from the substrate. The substrate containing the undesired material may optionally be contacted with carbon dioxide in the dense phase prior to and/or after the cavitation treatment to aid in removal of the undesired material. Further, spent liquid carbon dioxide may be treated to regenerate fresh liquid carbon dioxide, which is recycled to the cleaning chamber. Other gases besides carbon dioxide, which may be used, include nitrous oxide, sulfur hexafluoride, and xenon.
In a similar manner to that described in U.S. Pat. No. 5,316,591 quoted above, carbon dioxide, at a temperature below the critical temperature, is sprayed at close range on to accrued solids and, as the liquid is absorbed into the void-space of the solid mass, the rapid expansion caused by vaporization fragments and loosens the agglomerate.
With regard to chemical cleaning processes, a plethora of information, well known in the art, is available both in the literature and in technical brochures relating to chemical cleaning and chemically activated or detergent washing processes. Many such procedures utilize a solvent or carrier medium such as organic solvents or water together with acids, alkalis, suitable wetting agents/detergents and so on. These washing or rinsing processes give rise to several problems, not the least of which is disposal of effluent as well as the drying of the treated surfaces. There is, also, the risk of chemical reaction with the agglomerated material, giving rise, under certain conditions, to heat generation, undesirable gas emission or even explosions. Additionally, these processes are known to create a risk of chemical damage to the storage or handling equipment being treated. Furthermore these processes tend to be tedious and costly, and present another, perhaps more serious, difficulty, namely, disposal of the effluent or the cost of recovery of the agglomerated material.
The present invention seeks to provide an apparatus and method for effective cleaning and maintenance of storage, transport and handling vessels, directed to overcoming disadvantages of known art. More specifically, the present invention is directed to providing an apparatus and method for loosening and removing accretions of accumulated particulate solids from the vicinity of a vessel wall, particularly in a non-liquid environment. Additionally, the present invention is directed to providing environmentally friendly solutions for separating and breaking regions of bridging or rat-holing of agglomerated particulate solids across a vessel outlet, thereby to relieve blockages associated therewith.
In seeking to achieve the above objectives, and in accordance with a preferred embodiment of the present invention, suitable apparatus, for example, as described in the Applicant""s co-pending U.S. application Ser. No. 09/259,363, for generating shock-waves or gas impulses is provided and positioned in the vicinity of, or within, a gas-containing region of a vessel having an accretion of solids sought to be removed. The apparatus is operated so as to produce a series of shock waves or impulses which are propagated through the gas-containing portion of the vessel, thereby to loosen and progressively separate the agglomerated solids from surfaces of the vessel to which they are attached, or from regions of the vessel where they have accumulated.
There is thus provided, in accordance with a preferred embodiment of the invention, apparatus for dislodging an accretion of a substance from the vicinity of a vessel, the apparatus including:
apparatus for generating gas-borne shock waves in the vicinity of a vessel, thereby to expose a substance accrued on a surface thereof to separation forces causing at least partial separation of the substance from the surface, so as to facilitate removal of the at least partially separated substance therefrom; and
support apparatus for supporting the apparatus for generating shock waves in a selected association relative to the vessel.
Also, in accordance with a preferred embodiment of the present invention, there is provided a method for dislodging an accretion of a substance deposited in the vicinity of a vessel, the method including the steps:
mounting a source of gas-borne shock waves in a selected orientation with respect to a substance accrued on a facing surface of a vessel; and
operating the source of gas-borne shock waves so as to expose the accrued substance to separation forces, thereby causing at least partial separation of the accrued substance from the surface, so as to facilitate removal of the at least partially separated substance from the vessel.
Additionally, in accordance with a preferred embodiment of the present invention, the apparatus for generating gas-borne shock waves includes one or more gas impulse devices, which utilize compressed gas to generate gas-borne shock waves.
Further, and in accordance with one embodiment of the present invention, one or more gas impulse devices are adjustably suspended within a vessel adjacent to a substance accrued on an inward-facing surface thereof. The positions of the suspended one or more gas impulse devices are adjustable so that movement both vertically upward or downward and circumferencially within the vessel is facilitated, whereby proximity to accretion of solids is accomplished.
Furthermore, according to another variation of an embodiment of the present invention, one or more gas impulse devices are adjustably positioned adjacent to a substance accrued on an outward-facing surface.
A further variation in an embodiment of the present invention relates to apparatus in which one or more gas impulse devices are fixably attached into an orifice in a wall of a vessel and protruding into the interior thereof. Fixably mounting one or more gas impulse devices provides a facility for frequently eliminating accretion of solids as part of the operating cycle of a vessel or other solids handling equipment.
An additional variation in an embodiment of the present invention relates to apparatus in which one or more gas impulse devices include a compressed gas source fixably connected via a conduit thereto.
Another variation in an embodiment of the present invention relates to apparatus in which the compressed gas includes at least one gas selected from the group which may include, either alone or in any combination, air, nitrogen and carbon dioxide.
Frequently, for reasons of cost, convenience and availability, air is the selected compressed gas, generally supplied from an air compressor. However, in circumstances where reactivity between the oxygen in the air and the particulate solids give rise to a risk of explosion or fire, nitrogen or carbon dioxide are preferred although nitrogen is generally less expensive.
According to another embodiment to the present invention the method includes mounting a source of gas-borne shock waves in a selected orientation with respect to a substance accrued on an inward-facing surface of a vessel and includes fixably attaching the source of gas-borne shock waves within the inward-facing surface of the vessel.
According to an additional embodiment to the present invention the method includes mounting a source of gas-borne shock waves in a selected orientation with respect to a substance accrued on an inward-facing surface of a vessel and includes adjustably suspending the source of gas-borne shock waves within the vessel.
According to a further embodiment to the present invention, the method, in terms of which operating the source of gas-borne shock waves within the vessel, includes moving the source of gas-borne shock waves within the vessel thereby to expose a substance accrued on an inward-facing surface thereof to separation forces, causing at least partial separation of the substance from the inward-facing surface, so as to facilitate removal of the at least partially separated substance therefrom.
According to another embodiment to the present invention the method includes moving the source of gas-borne shock waves in the vicinity of an external surface of the vessel, thereby to expose a substance accrued on the external surface to separation forces causing at least partial separation of the substance from the external surface, so as to facilitate removal of the at least partially separated substance therefrom.
Additionally, according to an embodiment to the present invention the method includes operating the source of gas-borne shock waves by supplying a compressed gas to the source of gas-borne shock waves.
It will be appreciated by persons skilled in the art, that the apparatus and method of the present invention represents many advantages to a user in comparison to known art. For example, the present invention allows for cleaning of large or small vessels including silos, tanks, feed-hoppers, chimney-stacks, pipes, cyclones and many others, virtually irrespective of shape or accessibility. Performing the method of the invention is quick and cost-effective, and is relatively less labor intensive than methods of known art. The present invention also allows for low-cost, continuous or repeated cleaning of vessels on a regular basis or as is required. This aspect is especially relevant to materials or containers in which even a minimal accretion is undesirable. Additionally, the apparatus and method of the present invention reduces the risk of damage to a vessel being treated. Furthermore, the apparatus and method of the present invention eliminates the production of environmentally unfriendly by-products or effluents and substantially reduces the production of dust in the cleaning process. Since no flammable substances are employed, the present invention also reduces risk of explosion within a container being treated.